The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

Round 1

Reviewer 1 Report

The authors present a study case with a self defined impedance model, which is mathematically similar to ALS model, but more focus on the electrochemical parameters. With these values to be used such as the ionic conductivity, chemical capacitance etc., an alternative angle can be applied to predict and validate the designed cell structures.

The authors apply the model to fit the symmetrical cells with Ni/GDC anode, and the fitting results show promising results. Other reference are also cited to support the authors' method, and they are well accepted.

I think the authors are able to present a solid work correlating the mathematical model with experimental data. Though we have to admit the method used is not high novel, it still provides the insights of the microstructure and material properties of Ni/GDC anode. Therefore, I do recommend this manuscript to the Energies editor office.

Author Response

Dear Reviewer.

Thank you for carefully going through the manuscript.

We are pleased to hear your very positive overall statement. Minor adaptions to improve language and clearness of presentation were done in accordance with the requests by reviewer 4.

Reviewer 2 Report

This paper deals with the development of a theoretical description of electrochemical properties of anodic electrodes in SOFC. The topic is of quite high importance as the new generation of SOFC are supposed to rely on a full metal supported architecture, which operate at lower temperatures and therefore open efficiency issue for anodes too. The most comprehensive model of fuel cells electrodes was firstly proposed by Adler and co-workers some 20 years ago, but still this contribution is relevant and worth of attention because it approaches the microscopic description through electric parameters which can be easily accessed by impedance spectroscopy measurements. The paper both gives a sufficiently accurate derivation of equations and description of experiments supporting the validity of the model. The introduction is complete, the results are convincingly discussed and the conclusions are sound. It is recommended to publish this paper in the present form.

Author Response

Dear Reviewer.

Thank you for carefully going through the manuscript.

We are pleased to hear your very positive overall statement. Minor adaptions to improve language and clearness of presentation were made in accordance with the requests by reviewer 4.

Reviewer 3 Report

The paper "The relation of microstructure, materials properties 2 and impedance of SOFC electrodes: A case study of Ni/GDC anodes" is carefully written. The impedance analysis carried out is basic but very convincing. The paper presents a solid procedure of analyzing SOFCs. This paper should be published in Energies. Some careless mistakes are seen. The manuscript must be carefully rechecked, such as: Equations (16), (34) and Line 296: "*" should be avoided. Line 226: "LSC" and "LSCF" must be defilned.

Author Response

Dear Reviewer.

Thank you for carefully going through the manuscript.

We are pleased to hear your very positive overall statement.

We performed the the minor corrections requested by reviewer 3, and worked a bit on language and clearness of presentation, according to requests by reviewer 4.

Reviewer 4 Report

 This paper is quite interesting and is worth being published. Nevertheless, explanations are not so clear and convincing, resulting in difficulties to use it for non-specialists. For me, it is necessary to :

 

-1-Please clarify the 2.1. §. Indeed, authors use transmission line circuits to model porous electrodes. Nevertheless, it is not obvious that this model is more appropriate, to a physical point of view, than a series of R//CPE circuits. For non-specialists, it seems more obvious to describe phenomena with a series of circuits, because physically the different phenomena occur successively: adsorption, mass transfer, charge transfer, and conduction inside the electrolyte, and each phenomenon has a representative time constant. Perhaps the model chosen by authors is valid, but this choice is not enough commented.

 

-2-Authors give a mathematical treatment of the data, but some parameters, such as tortuosity, are not known (see for instance equation (4) or line 352 of page 10). There are other approximations : pressure: line 426 of page 12, homogeneity of porosity (§2.9 page 13), It is therefore confusing, because it seems that finally, it is possible to obtain a good fit between model and experimental data by adjusting these unknown parameters.

 

-3-Page 16, 1^st §: It seems that there is a mistake, or that an information is missing: how the 25mbar H2 + 25 mbar H2O mixture in Ar balance and pure 45mbar H2 + 25 mbar H2O can present a very similar partial pressure of reactive gases? Please clarify.

 

-4-Page 17, lines 579 to 583: It means that the capacitance, which is a fingerprint of phenomena, must be set as a fixed parameter. It is really confusing. Please clarify.

 

-5- Page 21, authors claim that the equivalent model is clearly supported (line 673). But we are not convinced that simulation with another model (for instance with series of CPE ou introduction of Warburg) is impossible.

 

-6-The conclusion must be clarified because it seems that in order to have a convinced fit, it is necessary to obtain others parameters, which can be obtained by other techniques, but also to electrochemical surface reaction rates, which remain unknown. And for non-specialists, the conclusion, claiming that this model allows optimization of SOFC electrodes but be developed: in the analysis proposed by authors, we just have determination of Rion and Rint, and the result is a fit of the entire diagram, but it would be also interesting to differentiate resistances due to the quality of electrolyte/electrode interface, or the pure diffusion phenomena.

 

I really think that this paper is really interesting, but some additional explanations are required before being published.

Author Response

Please see attachment

Author Response File: Author Response.docx